1. Field of the Invention
The present invention relates to a noise-testing method for a thin-film magnetic head with a magnetoresistive effect (MR) read head element to check whether the head produces noises, to a computer program product for testing a thin-film magnetic head with an MR read head element, and to a magnetic disk drive apparatus with a noise-test function.
2. Description of the Related Art
As hard disk drive apparatuses (HDD) increase in capacity and reduce in size, highly sensitive and high-resolution thin-film magnetic heads are being demanded. In order to satisfy the demand, giant magnetoresistive effect (GMR) thin-film magnetic heads with GMR read head elements each having a multi-layered structure with a magnetization-fixed layer and a magnetization-free layer become widely used. On the other hand, tunnel magnetoresistive effect (TMR) thin-film magnetic heads with TMR read head elements having higher sensitivity and higher resolution are put to practical use.
In thin-film magnetic heads with MR read head elements, defective products that generate Barkhausen noise in their outputs may be included. The Barkhausen noise is generated primarily because a magnetic domain wall is caught in defects in the magnetic film constituting the MR read head element as the magnetic domain wall moves, and is affected substantially by stress applied to the MR read head element. In practice, when an external or internal stress that exceeds a certain amount is applied, inverse magnetostriction disperses the magnetization in the MR read head element to destabilize the structure of the magnetic domains, making it more likely to cause Barkhausen noise. Such a stress can be caused by a distortion of the structure of the element itself as well as increase of deformation by the thermal expansion associated with an increase in the temperature of the element.
The influence of temperature and stress has become more remarkable than ever before especially in the aforementioned thin-film magnetic heads with MR read head elements each having the multi-layered structure.
Furthermore, in order to stably control the flying height of a thin-film magnetic head, which is set to an ultra-small value in a recent magnetic disk drive apparatus, a technique has come into adoption in which a heating element is provided within a thin-film magnetic head and the end of the head element is caused to be protruded in the direction of the magnetic disk by the heat generated by the heating element to adjust the flying height. U.S. Pat. No. 5,991,113, for example, discloses such technique. With this technique, thermal asperities and crashes are avoided to maintain good read and write characteristics. However, heat generated by such a heating element further heats the MR read head element and portions around the MR read head element, and can further increase the influence of the temperature and stress.
Approaches to preventing the Barkhausen noise in MR read head elements have been proposed. For example, Japanese Patent Publication No. 2002-133621A proposes a method for determining whether an MR read head element is acceptable or defective by measuring noise generated in response to various values of sense currents flowing through the MR element.
However, it has been very difficult to identify heads having the noise problem beforehand with the related art described above. Namely, even if a head was tested by using a sense current to cause an MR read head element itself to generate heat to induce thermal stress and was determined as non-defective heads, the head has sometimes caused Barkhausen noise under actual high-temperature conditions.
Furthermore, increasing the sense current value in order to test a head can cause an irreversible change in the MR effect element and make the testing a destructive test. This causes a serious problem especially in the case of a TMR effect element including a tunnel barrier layer, which is an ultra-thin insulation film.
In order to solve these problems, the assignee of this application has proposed, in U.S. patent application Ser. No. 11/835,049, filed on Aug. 7, 2007, a test method of a thin-film magnetic head having an MR read head element and a heating section capable of applying heat and stress to this MR read head element. According to this preceding test method proposed, characteristics of the MR read head element when the head is heated by applying an electrical power with a constant or gradually increasing value to the heating section is measured.
This test method can detect normal high-temperature noises that certainly occur when the environment temperature becomes high and disappear when the environment temperature returns. However, with respect to special kind of high-temperature noises that suddenly occur when the environment temperature becomes high and will not occur when a period under high temperature environment is short, it is impossible to detect such special high-temperature noises without application of power for a long time. This causes to take a long time for determination whether a thin-film magnetic head is good product or not and therefore it is difficult to perform such test during a fabrication process of the thin-film magnetic head.